Japan's top weapons maker has confirmed it was the victim of a cyber attack reportedly targeting data on missiles, submarines and nuclear power plants.
Mitsubishi Heavy Industries (MHI) said viruses were found on more than 80 of its servers and computers last month.
The government said it was not aware of any leak of sensitive information.
But the defence ministry has demanded MHI carry out a full investigation. Officials were angered after learning of the breach from local media reports.
